Handwriting has already been studied in a static manner by graphology. However there are cases in which graphological analysis is inadequate or liable to mistakes and a dynamic analysis of the writing must be used. This requirement is increasingly necessary in order to authenticate signatures during the endorsement or issue of a cheque for example, or for payments or withdrawals of money by means of credit cards or travellers' checks which are being used more frequently.
Various solutions have already been proposed for dynamic analysis of writing, in particular for comparing two apparently similar signatures in order to ascertain whether they have been produced by the same person.
It has already been proposed for this purpose to measure the contact pressure of the pen on the writing support, and the lateral friction between the pen and the writing support. The drawback of these two proposals is that they are strongly influenced by the type of instrument used for writing as well as by the type of writing support, so that the information obtained by these methods may show wide variations between the analysis of two signatures made by the same person under different material conditions.
It has also been proposed to measure the successive accelerations during writing by means of accelerometers fixed to the writing instrument. The drawback of this solution is due to its dependence on the spatial arrangement of the accelerometers. In effect, as the writing instrument is generally of a cylindrical form, the accelerometers may be in any position about the axis when the instrument is picked up. Consequently, the accelerations recorded may vary considerably between two signatures made by the same person.